Questions about Ph and Infection

Anders Gorm Pedersen gorm at
Fri Jun 2 09:25:06 EST 2000

browning70 at wrote:

> To begin, it is my understanding that most pathogens have a weak
> negative charge.  There are people who claim agents such as Colloidal
> Silver are effective against antigens because they carry a positive
> charge. Silver has been used as an antimicrobal for certain, especially
> Silver Nitrate also Silver Sulfadiazine.
> I am just trying to understand how Colloidal Silver would work in-
> vivo.  I am forgetful of my High School Chemistry, but what happens
> when the positively colloidal Silver hits the stomach acid.  Is not an
> acid an electron Donor (meaning it has a negative charge)? Would the
> stomach acid neutralize a positively charged ion?

Dear Rob, 

I will return to your technical questions below, but first some comments
on the use of colloidal silver.

Silver compounds (e.g., silver nitrate) currently have very limited use
as antiseptics, especially for burn wounds and as prohylactic treatment
of infant eye infections. They are always applied externally, not
ingested. Historically, silver compounds HAVE been used for their
antibacterial effects, but they have now been almost completely replaced
by more efficient and less toxic compunds. 

In the last ten years or so, there has been very aggressive marketing of
colloidal silver (and other metals) for the treatment of an amazing
range of diseases including AIDS, cancer, cystic fibrosis, diabetes,
etc. Colloidal silver has also been claimed to have a beneficial effect
on the immune system and is marketed as a dietary supplement. There is,
however, no solid scientific evidence for these effects, and the FDA has
issued a final rule declaring that all over-the-counter (OTC) drug
products containing colloidal silver or silver salts are not recognized
as safe and effective and are misbranded:

One interesting, but highly unpleasant, result of using silver compounds
is a condition known as argyria - a discoloration of the skin caued by
silver deposits:

It would be wonderful if there existed drugs that really were able to do
all the things ascribed to colloidal silver, but unfortunately that
seems not to be the case. In fact, the long list of diseases it can 
putatively cure, should make you suspicious. The only ones benefitting
from colloidal silver and similar products are probably the people
selling it. It is, of course, understandable that persons who are
afflicted with diseases
that are difficult or impossible to treat, turn to these products (and
I'm guessing that you had trouble getting rid of your Lyme disease?).
Below I've listed several websites that deal with colloidal silver and
the claims made about it. At the end of this email I've furthermore
included a letter from JAMA (Journal of the American Medical
Association) warning about the use of these products.

Regarding the technical questions: 

First, the antimicrobial action of silver is not merely caused by the
charge of silver ions (if that was the case, then the sodium in ordinary
salt would presumably have the same effect). It is not completely clear
how silver works, but it is apparently connected to its effect on
proteins present on the bacterial surface.

An acid is defined as a molecule that can donate protons, i.e.,
positively charged elementary particles. Nitrate is a weak base and may
react with the acidic stoamch contents. Nothing much will happen to the
silver ions (if I remember my chemistry correctly).

As for the surface charge: There are very many different types of
pathogens, and every individual one has different surface properties.
Bacteria, for instance, are covered with many different proteins,
lipids, and polysaccharides, each with different chemical properties.
Some of these molecules have a negative charge, others are positively
charged, and some have practically no charge at all. It is not clear
that there is a general trend for the net charge of pathogens, and there
are good reasons why there shouldn't be: importantly many pathogens rely
interacting with specific "receptors" on the surface of the cell they
are invading. Depending on the chemical properties of this receptor, it
might be beneficial for the invading pathogen to be either negatively or
positively charged, or alternatively to be hydrophobic (and therefore
uncharged). The surface properties of microbes will also depend on the
growth conditions, especially availability of nutrients and pH of

There are a number of investigations of how surface properties interfere
on adherence and infectivity. Some pathogens have positive charges, some
have both positive and negative, some have negative, and some have none.
In some cases the charge has an effect on adherence or invasion, in some
cases there is no effect. E.g. see:

J Med Microbiol 1990 Apr;31(4):259-70, Surface-associated properties of
Streptococcus milleri group strains and their potential relation to
pathogenesis.  Willcox MD, Knox KW 

Infect Immun 1990 Sep;58(9):3056-60, In vitro surface properties of the
newly recognized gastric pathogen Helicobacter pylori. Smith JI, Drumm
B, Neumann AW, Policova Z, Sherman PM

Int J Food Microbiol 1999 Dec 15;53(2-3):185-93, The effects of the
surface charge and hydrophobicity of Escherichia coli on its adhesion to
beef muscle. 
Li J, McLandsborough LA 

J Virol 2000 May;74(10):4474-82, An evolutionarily conserved positively
charged amino acid in the putative membrane-spanning domain of the foamy
virus envelope protein controls fusion activity. Pietschmann T, Zentgraf
H, Rethwilm A, Lindemann D 

Hope this helps,

 Anders Gorm Pedersen, cand.scient., Ph.D.  (gorm at

 Center for Biological Sequence Analysis
 Technical University of Denmark
 Bldg 208, DK-2800 Lyngby, Denmark

 phone: (+45) 45 25 24 84
 fax:   (+45) 45 93 15 85


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